This invention relates to a safety fence surrounding a hatch provided in a slab of a multi-story building.
In such multi-story buildings as power plants, hatches are provided in the slab of each floor, through which necessary equipment and materials are brought in and taken out. When not used, such hatches are closed by lids.
In order to bring in or take out a certain article, the lids covering the hatches are removed by an overhead crane installed on the rooftop; safety fences are set up around the now open hatches; and the intended article is brought in or taken out. The hatches are then closed and the fences are removed in reverse order.
For this operation, three men are needed, i.e., a crane operator and two additional men positioned near each hatch. The working time for each hatch by three men is about 25 minutes. In order to bring articles into or take them out of a lower floor, all the hatches above this floor have to be opened and then closed in the abovementioned manner. Work efficiency is thus extremely low.
When safety fences are set up around hatches with the hatches open, men or articles might fall into the hatches. Setting up of safety fences is time-consuming and troublesome. Thus, workers frequently omit setting up fences, knowing that this is dangerous.
In order to solve this problem, unexamined Japanese utility model publication 5-57243 proposes a hatch/safety fence structure comprising lids and side frames mounted on each hatch formed in a slab. In a normal state, the hatch is closed by the lids and the frames. When the lids and the frames are raised to open the hatch to bring in or take out articles, the lids and the frames are automatically assembled into a safety fence.
This safety fence has counterweights so that the lids can be easily erected. The counterweights are supported by shafts extending between the opposed sides of the hatch. Thus, the effective area usable when articles are brought in or taken out through the hatch is limited to the area defined between the shafts.
If the ceiling of the floor in which the hatches provided is low, it may be impossible to bring in or take out an article because the article cannot be lifted to a level higher than the top of the fence.
In addition, the fence prevents an operator from entering the hatch even if he has to.
Furthermore, in order to prevent men from falling into the hatch over the fence, the fence has to be at least about 110 cm high. But if the hatch is small, the safety fence, set up by erecting the lids and side frames of such a hatch may be lower than 110 cm.
An object of this invention is to provide a safety fence which permits effective use of the opening of the hatch, makes it possible to bring in and take out an article even if the ceiling is low, permits access into the hatch, and is high enough even if the hatch is small.